"lets you browse the apps your friends use" & "If a mobile app requires a download, you’ll be sent to install it from the Apple App Store or Google Play."

Are they anything more than a filter on the existing app stores based on my friends usage? What is my motivation as a user to install their app store?

Also, I checked the Privacy settings on my Facebook account and it is not clear how to ensure my app usage is not shared with others. Features first, respect of users' privacy last.